Froth flotation is one of the most widely used processes for beneficiating ores containing valuable minerals. It is especially useful for separating finely ground valuable minerals from their associated gangue or for separating valuable minerals from one another. Flotation is based on the affinity of suitably prepared mineral surfaces for air bubbles. A froth or a foam is formed by introducing air into an agitated pulp of the finely ground ore in water containing a frothing or foaming agent. A chief advantage of separation by froth flotation is that it is a relatively efficient operation at a substantially lower cost than many other processes.
Current theory and practice state that the success of a sulfide flotation process depends to a great degree on the reagent(s) called collector(s) that impart(s) selective hydrophobicity to the value sulfide mineral that has to be separated from other minerals. Thus, the flotation separation of one mineral species from another depends upon the relative wettability of mineral surfaces by water. Typically, the surface free energy is purportedly lowered by the adsorption of heteropolar collectors. The hydrophobic coating this provides acts in this explanation as a bridge so that the mineral particles may be attached to an air bubble. The practice of this invention is not, however, limited by this or other theories of flotation.
In addition to the collector, several other reagents are necessary. Among these, frothing agents are used to provide a stable flotation froth, persistent enough to facilitate the mineral separation, but not so persistent that it cannot be broken down to allow subsequent processing. The most commonly used frothing agents are pine oil, creosote, cresylic acid and alcohols such as 4-methyl-2-pentanol, polypropylene glycols and ethers, etc.
Moreover, certain other important reagents, such as modifiers, are also largely responsible for the success of flotation separation of sulfide minerals. Modifiers include all reagents whose principal function is neither collecting or frothing, but one of modifying the surface of a mineral so that a collector either adsorbs to it or does not. Modifying agents can thus be considered as depressants, activators, pH regulators, dispersants, deactivators, etc. Often, a modifier may perform several functions simultaneously. Current theory and practice of sulfide flotation suggest that effectiveness of all classes of flotation agents depends to a large extent on the degree of alkalinity or acidity of the ore pulp.
The development of neutral derivatives of xanthates such as alkyl xanthogen alkyl formates are disclosed as sulfide collectors are known in the art and are disclosed in, for example, U.S. Pat. No. 2,412,500. In the '500 patent, alkyl xanthogen formates which are unsymmetrical with respect to the alkyl radicals are shown to be highly effective flotation reagents which may be employed advantageously as mineral collecting agents in conjunction with frothing agents and conditioning agents in froth flotation operations. Other structural modifications of the general structure were disclosed in U.S. Pat. No. 2,608,572, for example, alkyl formate substitutents containing unsaturated groups. In U.S. Pat. No. 2,608,573, the alkyl formate substitutents described contain halogen, nitrile and nitro groups. Bis alkyl xanthogen formates are described as sulfide collectors in U.S. Pat. No. 2,602,814. The '814 patent provides dicarbonyl compounds comprising organic dithio acid radicals and dicarbonyl compounds in which the carbonyl groups are joined together by means of multivalent organic radicals.
Another class of sulfide collectors which have obtained some degree of commercial success in froth flotation are oily sulfide collectors comprising dialkylthionocarbamate or diurethane compounds. In U.S. Pat. No. 2,691,635, a process for making dialkylthionocarbamates is disclosed. In U.S. Pat. No. 3,907,854, an improved process for making dialkylthionocarbamates is described. In U.S. Pat. No. 3,590,998, a thionocarbamate sulfide collector structure in which the N-alkyl substitutent is joined by alkoxycarbonyl groups is disclosed. In Reissue U.S. Pat. No. 32,786, collector compositions for use in froth flotation processes using hydrocarboxycarbonyl thiourea is described. These patents are incorporated herein by reference.
The synergistic use of the mixtures of dialkylthionocarbamates and dithiophosphates has been disclosed as collectors for the recovery of copper from copper containing ores in U.S. Pat. No. 3,925,218 and the synergistic use of the mixtures of allylalkylthionocarbamates and dithiophosphates for the recovery of platinum group metals and gold is taught in U.S. Pat. No. 5,232,581. These patents however, do not include xanthate nor do they recognize the synergistic effects of allylalkylthionocarbamates and xanthates.
Although the use of dialkylthionocarbamates and xanthates separately may be used as collectors in flotation of sphalerite, there is a need for other chemical formulations that provide greater efficiency in this process.
Accordingly, it is an object of the present invention to provide a new and improved sulfide collector and flotation process for the beneficiation of sulfide minerals employing froth flotation methods.